In plain words
The day we root out Ahaṅkāra with the Buddhi: that day is the slaying of Narakāsura
In this Navarātri, holding that the Devī took form as Chāmuṇḍeśvarī and slew Narakāsura, they keep this tenth day as Vijayadaśamī and worship Chāmuṇḍeśvarī. Long ago one called Naraka was the leader of all the rākṣasas. That is, the leader of all bad qualities, all evil thoughts, all evil intent. The leader of them all is Ahaṅkāra! So on this day we must slay the Naraka called Ahaṅkāra. In the name Chā-muṇḍī, muṇḍī means the head. They said ‘Muṇḍe muṇḍe matirbhinnaḥ’. That is, each one's head is of its own kind. That is, in the heads of different people different evil thoughts arise. Through the Buddhi we must slay this Ahaṅkāra that is these bad qualities. The day we root out Ahaṅkāra with the Buddhi: that very day is the slaying of Narakāsura. Looking at all this in an outward way, we set up an image of Chāmuṇḍeśvarī and worship it. That Chāmuṇḍī is in our own muṇḍī. That is, she is in our own head. How can we bring the Chāmuṇḍī who is within us from somewhere outside and pray to her? Even if we worship in that way, we must feel it as reflection of the inner being, that is: ‘I am doing outside only what is within.’ These Navarātri days teach these inner meanings above all. Jñāna is not a thing someone hands over; nor is it something got from elders. We must gain it by our own effort alone. How? We must teach everything to the mind. What use is teaching the man? The man listens and forgets. We must teach the mind. Only when the mind is taught can the man change. Today the man changes, but the mind does not change. All the teaching given today and all we hear today we gather in only as far as the man; it does not reach the mind.